// ASM: a very small and fast Java bytecode manipulation framework
// Copyright (c) 2000-2011 INRIA, France Telecom
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions
// are met:
// 1. Redistributions of source code must retain the above copyright
//    notice, this list of conditions and the following disclaimer.
// 2. Redistributions in binary form must reproduce the above copyright
//    notice, this list of conditions and the following disclaimer in the
//    documentation and/or other materials provided with the distribution.
// 3. Neither the name of the copyright holders nor the names of its
//    contributors may be used to endorse or promote products derived from
//    this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
// THE POSSIBILITY OF SUCH DAMAGE.
package cn.taketoday.context.asm;

/**
 * A non standard class, field, method or code attribute, as defined in the Java
 * Virtual Machine Specification (JVMS).
 *
 * @author Eric Bruneton
 * @author Eugene Kuleshov
 * @see <a href=
 * "https://docs.oracle.com/javase/specs/jvms/se9/html/jvms-4.html#jvms-4.7">JVMS
 * 4.7</a>
 * @see <a href=
 * "https://docs.oracle.com/javase/specs/jvms/se9/html/jvms-4.html#jvms-4.7.3">JVMS
 * 4.7.3</a>
 */
public class Attribute {

  /** The type of this attribute, also called its name in the JVMS. */
  public final String type;

  /**
   * The raw content of this attribute, only used for unknown attributes (see
   * {@link #isUnknown()}). The 6 header bytes of the attribute
   * (attribute_name_index and attribute_length) are <i>not</i> included.
   */
  private byte[] content;

  /**
   * The next attribute in this attribute list (Attribute instances can be linked
   * via this field to store a list of class, field, method or code attributes).
   * May be {@literal null}.
   */
  Attribute nextAttribute;

  /**
   * Constructs a new empty attribute.
   *
   * @param type
   *         the type of the attribute.
   */
  protected Attribute(final String type) {
    this.type = type;
  }

  /**
   * Returns {@literal true} if this type of attribute is unknown. This means that
   * the attribute content can't be parsed to extract constant pool references,
   * labels, etc. Instead, the attribute content is read as an opaque byte array,
   * and written back as is. This can lead to invalid attributes, if the content
   * actually contains constant pool references, labels, or other symbolic
   * references that need to be updated when there are changes to the constant
   * pool, the method bytecode, etc. The default implementation of this method
   * always returns {@literal true}.
   *
   * @return {@literal true} if this type of attribute is unknown.
   */
  public boolean isUnknown() {
    return true;
  }

  /**
   * Returns {@literal true} if this type of attribute is a code attribute.
   *
   * @return {@literal true} if this type of attribute is a code attribute.
   */
  public boolean isCodeAttribute() {
    return false;
  }

  /**
   * Returns the labels corresponding to this attribute.
   *
   * @return the labels corresponding to this attribute, or {@literal null} if
   * this attribute is not a code attribute that contains labels.
   */
  protected Label[] getLabels() {
    return new Label[0];
  }

  /**
   * Reads a {@link #type} attribute. This method must return a <i>new</i>
   * {@link Attribute} object, of type {@link #type}, corresponding to the
   * 'length' bytes starting at 'offset', in the given ClassReader.
   *
   * @param classReader
   *         the class that contains the attribute to be read.
   * @param offset
   *         index of the first byte of the attribute's content in
   *         {@link ClassReader#b}. The 6 attribute header bytes
   *         (attribute_name_index and attribute_length) are not taken into
   *         account here.
   * @param length
   *         the length of the attribute's content (excluding the 6 attribute
   *         header bytes).
   * @param charBuffer
   *         the buffer to be used to call the ClassReader methods requiring a
   *         'charBuffer' parameter.
   * @param codeAttributeOffset
   *         index of the first byte of content of the enclosing Code attribute
   *         in {@link ClassReader#b}, or -1 if the attribute to be read is not
   *         a code attribute. The 6 attribute header bytes
   *         (attribute_name_index and attribute_length) are not taken into
   *         account here.
   * @param labels
   *         the labels of the method's code, or {@literal null} if the
   *         attribute to be read is not a code attribute.
   *
   * @return a <i>new</i> {@link Attribute} object corresponding to the specified
   * bytes.
   */
  protected Attribute read(final ClassReader classReader, final int offset, final int length, final char[] charBuffer,
                           final int codeAttributeOffset, final Label[] labels) {
    Attribute attribute = new Attribute(type);
    attribute.content = new byte[length];
    System.arraycopy(classReader.b, offset, attribute.content, 0, length);
    return attribute;
  }

  /**
   * Returns the byte array form of the content of this attribute. The 6 header
   * bytes (attribute_name_index and attribute_length) must <i>not</i> be added in
   * the returned ByteVector.
   *
   * @param classWriter
   *         the class to which this attribute must be added. This parameter
   *         can be used to add the items that corresponds to this attribute to
   *         the constant pool of this class.
   * @param code
   *         the bytecode of the method corresponding to this code attribute,
   *         or {@literal null} if this attribute is not a code attribute.
   *         Corresponds to the 'code' field of the Code attribute.
   * @param codeLength
   *         the length of the bytecode of the method corresponding to this
   *         code attribute, or 0 if this attribute is not a code attribute.
   *         Corresponds to the 'code_length' field of the Code attribute.
   * @param maxStack
   *         the maximum stack size of the method corresponding to this code
   *         attribute, or -1 if this attribute is not a code attribute.
   * @param maxLocals
   *         the maximum number of local variables of the method corresponding
   *         to this code attribute, or -1 if this attribute is not a code
   *         attribute.
   *
   * @return the byte array form of this attribute.
   */
  protected ByteVector write(final ClassWriter classWriter, final byte[] code, final int codeLength,
                             final int maxStack, final int maxLocals) {
    return new ByteVector(content);
  }

  /**
   * Returns the number of attributes of the attribute list that begins with this
   * attribute.
   *
   * @return the number of attributes of the attribute list that begins with this
   * attribute.
   */
  final int getAttributeCount() {
    int count = 0;
    Attribute attribute = this;
    while (attribute != null) {
      count += 1;
      attribute = attribute.nextAttribute;
    }
    return count;
  }

  /**
   * Returns the total size in bytes of all the attributes in the attribute list
   * that begins with this attribute. This size includes the 6 header bytes
   * (attribute_name_index and attribute_length) per attribute. Also adds the
   * attribute type names to the constant pool.
   *
   * @param symbolTable
   *         where the constants used in the attributes must be stored.
   *
   * @return the size of all the attributes in this attribute list. This size
   * includes the size of the attribute headers.
   */
  final int computeAttributesSize(final SymbolTable symbolTable) {
    final byte[] code = null;
    final int codeLength = 0;
    final int maxStack = -1;
    final int maxLocals = -1;
    return computeAttributesSize(symbolTable, code, codeLength, maxStack, maxLocals);
  }

  /**
   * Returns the total size in bytes of all the attributes in the attribute list
   * that begins with this attribute. This size includes the 6 header bytes
   * (attribute_name_index and attribute_length) per attribute. Also adds the
   * attribute type names to the constant pool.
   *
   * @param symbolTable
   *         where the constants used in the attributes must be stored.
   * @param code
   *         the bytecode of the method corresponding to these code attributes,
   *         or {@literal
   *         null} if they are not code attributes. Corresponds to the 'code' field of
   *         the Code attribute.
   * @param codeLength
   *         the length of the bytecode of the method corresponding to these
   *         code attributes, or 0 if they are not code attributes. Corresponds
   *         to the 'code_length' field of the Code attribute.
   * @param maxStack
   *         the maximum stack size of the method corresponding to these code
   *         attributes, or -1 if they are not code attributes.
   * @param maxLocals
   *         the maximum number of local variables of the method corresponding
   *         to these code attributes, or -1 if they are not code attribute.
   *
   * @return the size of all the attributes in this attribute list. This size
   * includes the size of the attribute headers.
   */
  final int computeAttributesSize(final SymbolTable symbolTable, final byte[] code, final int codeLength,
                                  final int maxStack, final int maxLocals) {
    final ClassWriter classWriter = symbolTable.classWriter;
    int size = 0;
    Attribute attribute = this;
    while (attribute != null) {
      symbolTable.addConstantUtf8(attribute.type);
      size += 6 + attribute.write(classWriter, code, codeLength, maxStack, maxLocals).length;
      attribute = attribute.nextAttribute;
    }
    return size;
  }

  /**
   * Puts all the attributes of the attribute list that begins with this
   * attribute, in the given byte vector. This includes the 6 header bytes
   * (attribute_name_index and attribute_length) per attribute.
   *
   * @param symbolTable
   *         where the constants used in the attributes must be stored.
   * @param output
   *         where the attributes must be written.
   */
  final void putAttributes(final SymbolTable symbolTable, final ByteVector output) {
    final byte[] code = null;
    final int codeLength = 0;
    final int maxStack = -1;
    final int maxLocals = -1;
    putAttributes(symbolTable, code, codeLength, maxStack, maxLocals, output);
  }

  /**
   * Puts all the attributes of the attribute list that begins with this
   * attribute, in the given byte vector. This includes the 6 header bytes
   * (attribute_name_index and attribute_length) per attribute.
   *
   * @param symbolTable
   *         where the constants used in the attributes must be stored.
   * @param code
   *         the bytecode of the method corresponding to these code attributes,
   *         or {@literal
   *         null} if they are not code attributes. Corresponds to the 'code' field of
   *         the Code attribute.
   * @param codeLength
   *         the length of the bytecode of the method corresponding to these
   *         code attributes, or 0 if they are not code attributes. Corresponds
   *         to the 'code_length' field of the Code attribute.
   * @param maxStack
   *         the maximum stack size of the method corresponding to these code
   *         attributes, or -1 if they are not code attributes.
   * @param maxLocals
   *         the maximum number of local variables of the method corresponding
   *         to these code attributes, or -1 if they are not code attribute.
   * @param output
   *         where the attributes must be written.
   */
  final void putAttributes(final SymbolTable symbolTable, final byte[] code, final int codeLength, final int maxStack,
                           final int maxLocals, final ByteVector output) {
    final ClassWriter classWriter = symbolTable.classWriter;
    Attribute attribute = this;
    while (attribute != null) {
      ByteVector attributeContent = attribute.write(classWriter, code, codeLength, maxStack, maxLocals);
      // Put attribute_name_index and attribute_length.
      output.putShort(symbolTable.addConstantUtf8(attribute.type)).putInt(attributeContent.length);
      output.putByteArray(attributeContent.data, 0, attributeContent.length);
      attribute = attribute.nextAttribute;
    }
  }

  /**
   * A set of attribute prototypes (attributes with the same type are considered
   * equal).
   */
  static final class Set {

    private static final int SIZE_INCREMENT = 6;

    private int size;
    private Attribute[] data = new Attribute[SIZE_INCREMENT];

    void addAttributes(final Attribute attributeList) {
      Attribute attribute = attributeList;
      while (attribute != null) {
        if (!contains(attribute)) {
          add(attribute);
        }
        attribute = attribute.nextAttribute;
      }
    }

    Attribute[] toArray() {
      Attribute[] result = new Attribute[size];
      System.arraycopy(data, 0, result, 0, size);
      return result;
    }

    private boolean contains(final Attribute attribute) {
      for (int i = 0; i < size; ++i) {
        if (data[i].type.equals(attribute.type)) {
          return true;
        }
      }
      return false;
    }

    private void add(final Attribute attribute) {
      if (size >= data.length) {
        Attribute[] newData = new Attribute[data.length + SIZE_INCREMENT];
        System.arraycopy(data, 0, newData, 0, size);
        data = newData;
      }
      data[size++] = attribute;
    }
  }
}
